The US government on Sunday announced a federal investigation into the police response to the mass shooting at a Texas school five days ago as anger mounted over why armed officers waited more than one hour in the hall outside the classroom where the gunman killed 19 children and two teachers and wounded others.

The US Department of Justice said it will conduct a “critical incident review” of the law enforcement action in the small south Texas city of Uvalde last Tuesday.

“The goal of the review is to provide an independent account of law enforcement actions and responses that day, and to identify lessons learned and best practices to help first responders prepare for and respond to active shooter events,” DoJ spokesperson Anthony Coley said.

He noted that the mayor of Uvalde, Don McLaughlin, had requested the review.

Uvalde school district police chief Pedro Arredondo, who was in command of the incident response, in which state officials said failing to storm into the classroom where the gunman was barricaded was “the wrong decision”, remained out of sight and under police protection on Sunday.

Texas state senator Roland Gutierrez, a Democrat who represents Uvalde, said that errors in the response to the school shooting may have contributed to more deaths, and he had spoken with the mother of one child who had died from a single gunshot.

“The first responder that they eventually talked to said that their child likely bled out,” Gutierrez told CNN on Sunday morning. “In that span of 30 or 40 minutes extra, that little girl might have lived.”

“So many things went wrong, here,” he added, although he said responsibility should not be on one police officer.

“At the end of the day, everybody failed, we failed these children,” he said, including lawmakers failing to pass stricter gun safety laws.

The gunman who caused carnage at Robb elementary school was local 18-year-old Salvador Ramos, who had reportedly made violent threats on social media and boasted about guns.

He legally bought the assault rifle and hundreds of rounds of ammunition he took into the school.

During the time that he had locked and barricaded himself into a classroom with the children and their teachers, one child made at least six calls to the 911 emergency number to plead for help from police, even as officers were right outside.

Gutierrez said he had questions over the official timeline of events, including which agency was in charge of the response. Ultimately, it was federal agents from border patrol, not Uvalde’s school police department or the separate city police force that has a part-time tactical Swat team, that confronted the gunman and killed him.

This appeared to be against state protocols to “confront the attacker”rapidly.

Criticism of the law enforcement response came from both sides of the political divide. Texas Republican congressman Dan Crenshaw, a former Navy Seal, told CNN that “the fact that it took border patrol an hour later to come in and actually do the job for the police is pretty embarrassing.”

“It does seem clear protocols weren’t followed,” Crenshaw added. “So, let’s let the investigation play out, but it’s hard not to see how someone doesn’t get fired for this, for these very, very bad calls.”

On Friday, Steven McCraw, head of the Texas department of public safety, admitted that the delay in storming the classroom had been “the wrong decision”.

Lydia Torres, a neighbor of Arredondo, told the New York Post: “Pete [Pedro] Arredondo is a coward. He didn’t do his job. He failed the children. He is hiding in his home, requesting the PD [police department] patrol the area and guard his home day and night. He should come out and speak up.”

Florida congresswoman and former Orlando police chief Val Demings demanded a “complete investigation”, telling CBS “we have more questions than answers.”